ICSE Class 10 Java | Array Mastery Lec 9: Bubble Sort Technique & Program

Welcome to Lecture 9 of our Java series! After mastering Searching algorithms, we now move to the most vital part of the Array unit: Sorting.

In this session, we go through the Bubble Sort technique. You will learn the "Adjacent Comparison" logic, how to perform swapping using a third variable, and how to write a full-length ICSE-style program in BlueJ to sort student marks in both ascending and descending order.

📌 WHAT YOU WILL LEARN IN THIS SESSION:
-- The Concept of Swapping: Why a = b and b = a fails, and how to use a temporary variable t to exchange values correctly.

-- Bubble Sort Mechanism: Understanding the "bubbling" effect where the largest element moves to the rightmost position in each iteration.

-- Dry Run & Iterations: Tracing an array of elements (50, 10, 1, 5, 30) to see how the list changes after each pass.

-- The Nested Loop Logic: - Outer Loop: Controls the number of passes.

Inner Loop: Handles the actual comparisons.

Crucial Syntax: Why we use j less than a.length - 1 to prevent ArrayIndexOutOfBoundsException.

-- Ascending vs. Descending: How to switch the sorting order by simply changing the relational operator.

-- Sorting Strings: A quick guide on using the compareTo() method for alphabetical sorting.

🕒 TIMESTAMPS:
00:00 Introduction to Sorting Algorithms
01:32 What is Swapping? (The 3-variable logic)
04:11 Bubble Sort Working & Mechanism
06:50 Step-by-Step Iteration Example
10:51 Writing the Program: Dynamic vs. Static Arrays
13:22 Explaining the "length - 1" logic in the Inner Loop
15:30 The Swapping Code inside the Loop
18:02 BlueJ Compilation and Output Demo
18:50 Changing to Descending Order
20:00 Logic for String Sorting (Alphabetical)
21:00 Final Tips for Section A Exam Questions

💡 KEY EXAM TAKEAWAYS:
SECTION A TRAP: Often, the board asks for the state of an array after the "2nd Iteration." Make sure you know how to trace the swaps manually!

INNER LOOP BOUNDARY: Always ensure your inner loop condition is j less than length - 1. Because you compare j with j + 1, going all the way to length will cause the program to crash.

STRING COMPARISON: For strings, remember to use a[j].compareTo(a[j+1]) greater than 0. You cannot use the greater than symbol directly on String objects.

📝 PRACTICE TASK:
Write a program to input 10 names into an array and sort them in Alphabetical Order using Bubble Sort.

Bonus Question: After the 1st iteration of Bubble Sort on the array [20, 10, 40, 5, 30], what will be the resulting order? Post your answer in the comments! 👇

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